In Adventure Time, the Great Mushroom War was responsible for the near extinction of Humans in the land of Ooo, but what was the cause of the Great Mushroom War? What were the chain of events that lead to this happening? Has this been revealed yet?

Answers are appreciated.

Note: I have tried google searching and going on the official adventure time wikia, but have found no information on the cause, not sure if it has been explained or not on how the Great Mushroom Wars started. If you know, please answer.

We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

I think the cause is not known yet. But adventure time is still in production and there are long term plans to reveal more and a movie to come, so we may know one day.
– Jeremy FrenchNov 18 '15 at 18:02

6 Answers
6

It's never directly explained what caused the Great Mushroom War, and nobody knows if they will ever reveal why there was a war in the first place, considering the show takes place 1,000 years after that took place.

The relevant information was that there was a single bomb that was supposed to end the war, the giant bomb that Simon (aka Ice King) stopped using his ice powers. This was shown in the season 5 stories Finn the Human and Jake the Dog where they wished that the Lich never existed. Stated here in the wikia:

The war likely ended when the mushroom bomb was dropped along with the
other nuclear weapons. This is evident from the episodes "Finn the
Human" and "Jake the Dog" when Finn wishes the Lich, a product of the
mushroom bomb, to have never existed. When the wish is granted, Finn
is transported to a world where Simon sacrifices himself to stop the
mushroom bomb and freezes the entire Earth in the process. Despite
some destruction, without the detonation of the mushroom bomb,
humanity would continue to exist. Also, in "Finn the Human," Farmworld
Marceline suggests that the mushroom bomb likely concluded the war as
she states that the world would have been annihilated if Simon had not
stopped the bomb with his ice powers.

It's also possible that Bravest Warriors (a cartoon by the creator of Adventure Time) and Adventure Time are connected in some way, considering that Chris, when looking into the future, saw a quick image of the Earth with a chunk of it missing. It looks almost exactly like the Earth in Adventure Time.

Bravest Warriors quick image

Picture of the Earth from Adventure Time

If the two are connected perhaps Bravest Warriors will explain how the Mushroom War starts on Earth and then leads to Adventure Time?

According to the wikipedia article Bravest Warriors is already set in the year 3085, don't the remains we see of the the world before the Great Mushroom War suggest it happened our own near future (or that of a world much like our own)?
– HypnosiflJan 15 '15 at 22:47

It's all hypothetical we are simply drawing at straws by connecting two things that were similar in both aka the depiction of Earth.
– DoctorWho22Jan 16 '15 at 0:12

The great mushroom war concluded with the dropping of the bomb, which produced the lick, likely took the chunk out of earth, and turned many humans into zombies. It probably also caused lots of natural disasters, and it probably created many of the magical creatures that exist afterwards. After all, in the episode Simon and Marcy, it is revealed that princess bubblegum was formed in a destroyed city with radioactive zombies.
– Xandar The ZenonJan 15 '16 at 21:16

During an exclusive interview with the show's creator, Pendelton Ward, he revealed that there was no cause to the war, they didn't even intend for adventure time to be casted in a post-apocalyptic setting. There was evidence supporting the post-apocalyptic theory in the episode "Businessmen," and the creators just took off with that idea, implying it in many episodes, and later making episodes solely based on that theory.

WARD: "I never planned it – I just saw this world as a magical place. The show developed organically – someone would add an element to the world, and it would stick. At some point, we did an episode about businessmen rising up from an iceberg at the bottom of a lake ("Business Time") and that made the world post-apocalyptic, and we just ran with it."

Probably Rachel was referring to this interview, where Ward says: " I never planned it – I just saw this world as a magical place. The show developed organically – someone would add an element to the world, and it would stick. At some point, we did an episode about businessmen rising up from an iceberg at the bottom of a lake ("Business Time") and that made the world post-apocalyptic, and we just ran with it."
– HypnosiflMar 8 '15 at 5:34

Well to be honest no one really knows (yet) how the mushroom war started but in the wiki and a few YouTube videos it's shown that while Simon (The Ice King) and Marceline were roaming around the ruined city there were several military vehicles with a red star on them suggesting they were either part of the Ukrainian, Russian or North Korean military.
I also found out that the war took place around the early 80s due to most of the old technology in adventure time episodes is from the 80s. Around that time (1982) there was a nuclear explosion in a Ukrainian city so the probably took place around Eastern Europe and Western Asia. In my opinion I think the war was fought between Ukraine, Russia and North Korea and the "Mushroom Bomb" was North Korean.
Source - https://m.youtube.com/watch?v=vdlLRH75GOM

Alright. I've been doing some reading, and the most popular theory is that Adventure Time is set in a post-apocalyptic Earth, with all humans either being mutated or killed off due to the detonation of the Mushroom Bomb. Well, scratch that. If you haven't seen "The Vault" it's the episode where Shoko appears, and we learn about her backstory. So we know that Shoko was around after the Mushroom War. Okay, what does that mean? Well, it actually means a lot. If Shoko was around after the bombing, born as a humanoid, then how can Finn be her incarnation? Humans were extinct, yet Finn was born supposedly as a 100% human. Impossible. How does this fit in with the theory that Adventure Time is post-apocalypse? It doesn't. It fits with the second most popular theory. That Finn is in a coma. All of the things that Pendelton Ward thought we couldn't figure out, we did. And that proves that a pre-teen is dreaming up the Land of Ooo, and that Finn is in a coma. The apocalypse never really happened in Adventure Time, it was simply dreamed up by a boy with a wild imagination, and who went through something awful. Also, some of the "mutated" humans cannot possibly ever truly be a mutation. I'm talking about Prismo. You all know him, if you're smart you hate him. Prismo is a being of an undetermined rank and an unknown type of life form. Is he even a life form, or just a spiritual being? Prismo is rarely even in the show, but as with Shoko, the most important characters are often the lamest. Prismo cannot possibly be a mutatation, as he is best classified as a being of pure energy with no weakness. (Yes that was a Gravity Falls reference.) Because of these small, but key pieces of evidence, it leads me to believe that this is the most plausible theory of Adventure Time. That Finn is in a coma. Don't kill me for adding this, but Finn could also be dreaming, and is simply asleep. Both of those theories fit this evidence. Okie-dokie-lokie, thanks for putting up with me for this long, bye!

~Rainbow Dash

So I did some more digging and found out some info about our favorite cartoon. Finn is not in a coma. He is not dreaming. The Mushroom War is not a real event, simply something Princess Bonnibel Bubblegum came up with to explain the crater in the Earth. Princess Bubblegum was the first mutation, a scientist accidentally mutating herself during an experiment. She mutated humans so she would not be alone, and decided to create the Candy Kingdom. She almost mutated Finn, but she couldn't. (What she did with Finn is similar to what she did to Flame Princess, that's why she refuses to start a romantic releshinship with him.) So, I personally don't believe this theory. We were discussing it at our most recent Awesome Animation Cartoon Club meeting. My friend, Lumpy Space Princess (We all take names from our favorite cartoon characters. I'm Rainbow Dash from My Little Pony.) came up with this theory herself. She thinks that Princess Bubblegum is 1,000,000% evil! and spends her time at our meetings trying to prove it to us. So, if you believe her theory, comment to let me know and I'll tell my friend that you agree with her.

~Rainbow Dash

Oh my glob!!! Thank you Hypnosifl, because of your constructive critism, I just realized something. If Prismo is just the dream of an old man, the old man looks human, that old man is African-American, and we know another old man who fits all of those criteria, I think that Mo is dreaming of Prismo, and that is the premise of adventure time. It would make a little sense, but then again there definitely are flaws in that theory. The old man seems to be in a different setting than the Mo Factory, and he's not hooked up to any machines. He also has a beard, but Mo does not. The more I think about this, the more I realize it makes no sense. Sorry!

When did they ever say humans were "extinct" in the flashbacks to Shoko's life in "The Vault"? Also, we know from the episode "Wake Up" that Prismo was (SPOILERS!) the dream of an old man in a cabin. And when you say you "found out some info about our favorite cartoon", can you link to where you found this theory?
– HypnosiflJan 15 '15 at 23:12

I just watched the episode "Wake Up" and I don't remember that, and they didn't say it in "The Vault" but if you pay attention to the series, Finn and Betty are the only humans who aren't mutated. By the way, when I said I "found out some more info about our favorite cartoon" it was just meant to be an attention grabber. But, thanks for your comment because I didn't think anyone would read this. Mathematical!
– user40631Jan 16 '15 at 20:15

1

"Wake Up" is online here, if you go to just after 8:25 (turn the volume up because it's quiet), Finn says "Wait, this old man is you?" and Prismo says "That's right, Prismo is nothing but the dream of a wrinkly old man." As for the origins of bubblegum, in the episode "Simon & Marcy" showing the time right after the Mushroom War, there's some bubblegum with a face, go to 10:35 - 10:45 here.
– HypnosiflJan 16 '15 at 20:47

Wait, maybe it wasn't "Wake Up." I don't remember the title. It was the episode when Finn and Jake are doing a death ritual for Prismo. With a pickle. As for the Princess Bubblegum thing, I had nothing to do with that. That's my friend's theory she came up with because she hates PB.
– user40631Jan 17 '15 at 1:47

Just so you know, I looked up the episode I watched, and it's called "Is That You?" Thank you for explaining my mistakes, Hypnosifl.
– user40631Jan 17 '15 at 23:12

I have a conclusion. I know what caused the Mushroom War. The land of Ooo is an aftermath of the Cold War. The Cold War was a state of political and military tension after World War II between powers in the Western Bloc and powers in the Eastern Bloc. Historians have not fully agreed on the dates, but 1947–1991 is common. I think in Adventure Time, when the Americans feared an attack from the Russians and the Russians feared an attack from the Americans, the Americans actually set off the nuclear missile and caused world war III. I have some proof too. Notice how Adventure Time's Earth has a hole. I don't know much about where places are on the Earth but it seems to me that that hole is where Russia used to be. And I know for a fact that the Americans had the missile. That is my statement and I am positive I am right.

Another thing to support that Russia was the hole in Adventure Time is Simon Petricov. I know 100% that Simon Petricov is a Russian name. Which means Simon must from be somewhere in Russia (although he could be from somewhere else but it is very unlikely). As you can see in the episode "Simon and Marcy" (which is possibly in Russia like I said earlier), there are nukes and destruction everywhere. Knowing that most of the destruction is in Russia, there is a strong chance that Russia is part of that hole.

" I know 100% that simon petricov is a russian name. Which means simon must be somewhere in russia. (although he could be somewhere else but it is very unlikely." you've never heard of emigrants? my family name is irish, but i'd have to go back 5 generations to find a family member who lived there.
– phantom42Sep 18 '15 at 18:30

Long ago almost 1000 to 2000 years ago their was a war against America Russia
And North Korea the Russians created this nuclear weapon that was suppose to end
Human life leaving the Russians alive but they didn't have time to finesh creating
This mass destruction of the world North Korea didn't like this idea nether did America who was supposed to be the hero the Russians couldn't let them take the bomb so the three countries went to war the Russians dropped the bomb on America
On a accident leaving America being destroyed and mutating the world around them
Creating a zombie plague in America spreading around the world.about 30/ of Americans including Finn and Simon and marcilen servived the Russians and the
Koreans still live and never to go to America because they fear of what they created.now after the war Simon and marcilen wonder around the destroyed city's
Of America but that ain't the end as a child marcilen got sick from a vampire virus
Flu and was turned into a vampire wile Simon and marceline were traveling they came across Betty, Simon's fiance. Betty and Simon had gotten into a argument when all of the sudden Simon put on the crown freezing the city around them scaring off Betty
But marceline kept on yelling at Simon to stop he finally calmed Down I have to go
Said Simon but why you're going to leave me again said marceline I hired someone to watch over you and Simon rode of on his sled leaving marceline alone as marceline
Grow up she has become a vampire hunter and that when she met Finn.

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